The leading U.S. trade negotiator exchanged unusually sharp words with his Canadian and Mexican counterparts Tuesday, saying he was “disappointed” at their “reluctance to give up unfair advantages.”

In a news conference wrapping up a fourth round of negotiations to revise the North American Free Trade Agreement, a combative U.S. Trade Representative Robert E. Lighthizer said the Trump administration was determined to craft a better deal for U.S. companies and reduce a roughly $60 billion trade deficit with Mexico.

“Trade deficits do matter, and we intend to reduce them,” Lighthizer said at a joint news conference with Minister of Foreign Affairs Chrystia Freeland of  Canada and Secretary of Economy Ildefonso Guajardo Villarreal of Mexico.

However, Freeland cautioned earlier that an agreement “cannot be achieved with a winner take all mind-set.” Guajardo said: “In order for the efforts of Mexico, the United States and Canada to be fruitful, we must understand that we all have limits.”

Despite the harsh words, the three ministers agreed to spread out the rounds of talks and extend them through the end of March, which Freeland called a sign of “goodwill.”

But there was little positive in the remarks beyond that.

Although NAFTA was designed to encourage investment and freer flow of goods between the three countries, Lighthizer said  “continuing to design a national manufacturing policy largely dependent on exports to the United States for balance cannot long continue.”

He added, “It is unreasonable to expect that the United States will continue to encourage … U.S. companies to invest in Mexico and Canada primarily for export to the United States.”

Freeland countered that U.S. proposals to increase U.S. national content in goods given favored treatment within NAFTA “would severely disrupt supply chains” and “put in jeopardy tens of thousands of jobs.”

She said that U.S. proposals “would turn back the clock on openness and predictability” and “in some cases run counter to World Trade Organization rules.”

She said “our purpose here is to make a good agreement even better,” but that what negotiators had seen was “a series of unconventional proposals” that “make our work much more challenging.”

Guajardo also appealed for reason. “Despite our current differences, we must ensure that the decisions we make today do not come back and haunt us tomorrow.”

Though President Trump has called NAFTA the “worst agreement ever,” he has heard from a cacophony of voices within the White House on how he should proceed on his trade threats.

White House National Economic Council Director Gary Cohn has tried to press Trump to be cautious, worried about what abrupt changes might mean for the U.S. and global economy. Commerce Secretary Wilbur Ross has focused much of his attention on dealing with what he views as trade imbalances between the U.S. and China, though some of those decisions have also been delayed as the White House has focused on NAFTA.

Lighthizer has emerged in recent weeks as one of the most strident voices within the White House, pushing back on foreign ministers and business groups who have urged caution. Peter Navarro, a top White House trade adviser, has lost his official senior perch within the Trump administration but remains very influential.

Damian Paletta contributed to this article.